78 GP bogging/stalling/shaking under load?

[naminator]

78 Grand Prix SJ with 307 Oldsmobile (Vin Y or Vin 9 with 5a heads, early 80's), is having some issues with doing anything under load. I have been working on the brakes, got a new caliper/pads/line on the front driver side, bled that side (I plan on refreshing/bleeding them all and have the passenger caliper/pads) and decided to check for leaks in my handy work. I shifted to drive and since the car is on a drive way that has a significant slope at the end, just shifting to drive let it roll forwards about 15 feet. Brakes barely stopped it, still working on that, but it did not leak. I shifted it into reverse and now, the car has the front tires lower than the rear and I needed to actually make the engine work to move backwards. Well it bogged and stalled as soon as it got to the "hump" in my driveway and needed some throttle. Put it in park, tried to start it up and it really did not like that. It refused to start, so I was messing with the choke cable and managed to eventually get it to idle, but it was also idling a lot slower than normal. Gave it some throttle, it perked up, so I dropped to idle and then shifted to reverse. It is a small space, so I gave it maybe half throttle, and the engine felt like it was trying to shake itself apart and no power. I gave it more throttle, the RPM increased and I just barely got it up over the hump and threw it in park.

I asked around and I was told it could be a few things. I know for a fact the trans, kick down cable is disconnected and fully shot, so that is on the list. The plugs are fouled and the previous owner messed up the firing order when doing "repairs", so the timing is probably off. Most days it starts the very first time, idles really smooth, but depending on the choke cable adjustment, it will idle very low and stall or it seems to idle fairly high. As I mentioned, timing is 100% going to be adjusted when I can get a timing light, plugs are being replaced and I am considering a re-build of the AVS2 1905 650cfm carb. I did spray carb cleaner, with an extension straw, around the base of the carb and any lines that may have a vacuum leak when the engine was at operating temp, but I didn't notice the idle speed increasing. Someone here suggested ripping out any and all, ancillary lines that are not required for the car to run, which I plan on doing, but maybe I am over complicating things.

If you did read that wall of text, I appreciate you putting up with my rambling train of thought. Otherwise I have a 307 Olds with an AVS2 1905 650cfm carb, disconnected kick down and under the slightest of loads the engine shakes stumbles and stalls.

 

[Supa.Slo.SS]

Did the car run ok before? Or is this your first time trying to get it running after the purchase from previous owner?

I would check everything associated with the distributor, i.e. wires, connections, vacuum lines, electrical plugs etc. I find it hard to believe that the timing would "move" if it was running good previously. If this is your first attempt of trying to get the car running from the previous owner, before you touch anything, I would make sure the wires are connected in the right order.

Also, check your fuel filter, not sure where its located on your car.

Kickdown cable, as I understand, drops down the gear when you smash down the throttle, i.e. your in 3rd gear smashed the throttle it drops the gear down to 2nd and the RPM shoot up to give the response. That being said good or bad the kickdown isn't going to cause the problem your describing IMO.

 

[ELCAM]

Sounds like a large vacuum leak. Check the power brake booster hose.

 

[pontiac guy]

This has nothing to do with your trans kickdown. I would bet money this is an ignition problem. You said your plugs are fouled. They are garbage. Either clean them or replace them. Are you sure you have the firing order right? Double check that. Then check the cap and rotor. Clean up the terminals with some medium sand paper. Then check the timing.

 

[naminator]

Did the car run ok before? Or is this your first time trying to get it running after the purchase from previous owner?

I would check everything associated with the distributor, i.e. wires, connections, vacuum lines, electrical plugs etc. I find it hard to believe that the timing would "move" if it was running good previously. If this is your first attempt of trying to get the car running from the previous owner, before you touch anything, I would make sure the wires are connected in the right order.

Also, check your fuel filter, not sure where its located on your car.

Kickdown cable, as I understand, drops down the gear when you smash down the throttle, i.e. your in 3rd gear smashed the throttle it drops the gear down to 2nd and the RPM shoot up to give the response. That being said good or bad the kickdown isn't going to cause the problem your describing IMO.

I have a fuel filter in between the pump and the carb. It is decent. I also drained the tank and put about 5g of fresh 94 octane in to offset anything that was still in the lines/tank that was old. Previous owner says it was running great and then suddenly not and he needed to floor it to make it move. He replaced the plugs/wires and tried to crank it a million times. He also hooked the wires in a clockwise not counter clockwise order, so I sorted that stuff out and it idles decent. I posted this about 2-3 weeks ago and since then cleaned all the plugs (they where fouled), fed it a can of seafoam down the carb, and sanded the contacts in the distributor a bit and hit them with electrical cleaner. It is definitely doing better and it is very likely a vacuum leak (which I think I found and resolved already). I also replaced all the old caps on the vacuum ports on the carb and it seems a lot better now.

Sounds like a large vacuum leak. Check the power brake booster hose.

I think, but haven't tested it, that a line that was hooked up amongst a mess of other lines was open. As far as I can tell, that would be the issue.

This has nothing to do with your trans kickdown. I would bet money this is an ignition problem. You said your plugs are fouled. They are garbage. Either clean them or replace them. Are you sure you have the firing order right? Double check that. Then check the cap and rotor. Clean up the terminals with some medium sand paper. Then check the timing.

Right firing order, cleaned the cap, cleaned the plugs and ones I sort it out running (still seems to run rich) I plan on replacing the plugs. Would rather not foul a new set of plugs when the current ones are "new" or at least 7 out of 8 are.

 

[olds307 and 403]

Almost guaranteed that carb needs recalibrated leaner for a 307. Also assume you adjusted the mixture screws. I also assume you have it timed around 20 degrees at idle with the vacuum advance plugged? I usually set my idle around 1000 rpm in park, more stable.

 

[Clone TIE Pilot]

Vacuum leaks generally affect idle more than high throttle / high load. Sounds more like a sticky or clogged needle valve or bad accel pump.

 

[naminator]

Almost guaranteed that carb needs recalibrated leaner for a 307. Also assume you adjusted the mixture screws. I also assume you have it timed around 20 degrees at idle with the vacuum advance plugged? I usually set my idle around 1000 rpm in park, more stable.

I have not configured the timing yet. I plan on getting a timing light this weekend and adjusting it properly. As for the mixture, it was set to what it was when I bought it. Currently it idles decently, starts easy enough, even with the choke wide open after sitting (needs an extra pump of the throttle and a bit more time cranking) but with the choke closed it starts every time.

Vacuum leaks generally affect idle more than high throttle / high load. Sounds more like a sticky or clogged needle valve or bad accel pump.

Well it idled the same with or without the vacuum lines plugged, which I figured was the issues, but when I plugged it, the brakes got a bit firmer and it was shifting better. I took it for a drive down the block again, after replacing (and bleeding) the passenger front caliper/pads and it was running pretty good. The only issue was when I really laid into the throttle hard, it would stumble. If it was at a lower RPM and I just stepped on it, it would stutter. If I rolled onto the throttle, it was fine and would accelerate easily enough, but really put the pedal down from either a stop/slow roll, it would do the stumble. I assume the carb is just dumping way too much fuel under full throttle?